The present invention generally relates to the field of scrim made up of a grid of warp threads and weft threads held in place by adhesive at the cross-points of the threads, said scrim being used in particular as reinforcement or support in various industrial applications.
The present invention more particularly relates to scrim formed by a grid of non-woven crossed or superposed threads, comprising at least two sheets of warp threads between which at least one sheet of weft threads is interposed, the warp and weft threads being bonded together at their cross-points by a binder creating a series of points of adhesive.
The present invention also relates to an industrial product, whether finished or otherwise, that incorporates therein scrim of the present invention.
The present invention also relates to a method of manufacturing scrim in which a grid of non-woven crossed or superposed threads is made comprising at least two sheets of warp threads between which at least one sheet of weft threads is interposed, and the grid of threads is coated in a binder to connect the warp and weft threads together.
It is known to make scrim, industrially that comprises a grid of non-woven crossed threads with the threads being stuck together at their cross-points by being impregnated with a binder, such as a thermoplastic adhesive, or the like. Known scrim such as that illustrated by way of example in FIG. 1 has at least two sheets of warp threads, A and B, that are superposed or offset, with each pair of sheets, A and B, having at least one sheet C of weft threads interposed therebetween. In those known embodiments, the warp threads 1 and the weft threads 2 are connected together at their cross-points 3 by a binder 4 creating a series of points of adhesive so as to obtain scrim presenting a structure that is finished and stable, mechanically speaking.
Scrim made using this technique generally provides satisfaction, and can be used as reinforcement or support in a wide variety of technical fields, for example such as in the building industry, as a support or backing for floors and ceramics or for wall coverings and fitted carpets, in the paper-making industry, or as a reinforcing element in synthetic or other foams.
Nevertheless, it has been found that presently known scrim suffers from certain drawbacks, and in particular a drawback associated with the relatively great and usually very irregular thickness of the scrim. The methods of manufacturing known scrim require mere coating using an adhesive or a thermoplastic binder of the PVC or PVA type, for example, without any other operation. As a result the scrim that is obtained is relatively thick regardless of its nature, its type, or the number of threads used, and this leads to the resulting scrim being relatively inflexible. In addition, the thickness of known scrim is particularly irregular because of the existence of portions in relief at the cross-points between the warp threads 1 and the weft threads 2. The presence of such irregularities in prior art scrim clearly gives rise to various drawbacks, industrially speaking, particularly for certain specific applications.
Furthermore, it has been found that conventional scrim presents a certain amount of weakness in the grid of threads stuck together at the cross-points between the warp threads and the weft threads.
Finally, prior art scrim consumes a relatively large amount of adhesive or thermoplastic binder, particularly if it is desired to attempt to reinforce the mechanical strength of the grid of threads at the cross-points. This leads to an increase in the cost of the resulting product, which constitutes a drawback, industrially speaking.
In an attempt to remedy at least some of these drawbacks, proposals have been made, such as in British Patent No. 1,463,969, to make thin scrim in which the grid of threads is redistributed by compression, in particular by calendaring the scrim in order to flatten it. The resulting calendared scrim does indeed possess a reduced thickness, e.g. by about 200 micrometers (xcexcm) to 150 xcexcm, compared with conventional scrim. However, such a reduction in the thickness of scrim by calendaring is accompanied by partial destruction of the structure of the points of adhesive between the warp and weft threads, such that the mechanical breaking strength of these points is greatly reduced compared with conventional scrim. Furthermore, the technique of compressing scrim by calendaring is not accompanied by a reduction in the quantity of adhesive used. In all, calendared scrim, apart from being relatively complex and difficult to obtain on an industrial scale, suffers from various drawbacks making its use limited or even inappropriate in some applications.
Consequently, one object of the present invention is to remedy the various above-mentioned drawbacks of prior art scrim and to provide novel scrim comprising a grid of non-oven crossed or superposed threads, the scrim having a thickness that is generally reduced and regular, and also presenting good mechanical strength while being of low manufacturing cost.
Another object of the present invention is to provide a novel scrim presenting general performance characteristics that are particularly high with respect to mechanical strength, flexibility, and bulk.
Another object of the present invention is to provide a novel scrim of a thickness that is particularly small and regular.
Another object of the present invention is to provide a novel industrial product incorporating scrim of the present invention.
An additional object of the present invention is to provide a novel method of manufacturing scrim comprising a grid of non-woven crossed or superposed threads that is particularly simple to implement.
In accordance with the present invention, these and other objects have now been realized by the invention of a scrim comprising a first sheet of non-woven warp threads, a second sheet of non-woven warp threads, and a third sheet of non-woven crossed weft threads interposed between the first and second sheets of non-woven warp threads, whereby the warp threads and the crossed weft threads include cross points where the warp and weft threads cross each other, and a binder binding together the warp and weft threads at the cross points thereby creating a plurality of adhesive points therebetween, the scrim having a performance ratio, TP, of greater than 30, the performance ratio represented by the formula   TP  =            S              T        xc3x97        E        xc3x97        C              xc3x97    100  
wherein S comprises the surface area of the adhesive points in mm2, T comprises the fineness of the warp and weft threads in g/km, E comprises the mean thickness of the scrim in mm, and C comprises the fraction of the adhesive binder in the scrim from 0 to 1. Preferably the performance ratio, TP, is from 45 to 120.
In accordance with one embodiment of the scrim of the present invention, the mean thickness, E, of the scrim is substantially regular across the entire surface of the scrim. Preferably, the mean thickness, E, is less than 0.175 mm, more preferably less than 0.150 mm, and most preferably from 0.150 to 0.06 mm.
In accordance with another embodiment of the scrim of the present invention, the fraction of the adhesive binder in the scrim, C, is less than 0.35.
In accordance with another embodiment of the scrim of the present invention, the warp and weft threads comprise glass threads. Preferably, the glass threads have a fineness, T, of from 5.5 to 136 g/km.
In accordance with another embodiment of the scrim of the present invention, the adhesive binder comprises a thermoplastic adhesive.
In accordance with another embodiment of the scrim of the present invention, the scrim is attached to a woven or non-woven fabric.
In accordance with the present invention, a method of manufacturing the scrim is provided comprising producing a grid of non-woven warp and weft threads by applying a first sheet of non-woven warp threads, applying a third sheet of non-woven crossed weft threads thereon, and applying a second sheet of non-woven warp threads thereon, whereby the warp threads and the crossed weft threads include cross points where the warp and weft threads cross each other, impregnating the grid with an adhesive binder for binding the warp and weft threads together at the cross points, and pressing the grid including the adhesive binder before the adhesive binder has concluded drying. Preferably, the pressing of the grid occurs at least partially simultaneously with the drying of the adhesive binder.
In accordance with the present invention, a laminated industrial product has been provided in combination with the scrim set forth above.
The objects of the present invention are achieved by means of scrim formed by a grid of non-woven crossed threads comprising:
at least two sheets of warp threads between which at least one sheet of weft threads is interposed,
the warp and weft threads being bonded together at their cross-points by means of a binder that creates a series of adhesive points,
wherein the scrim has a performance ratio TP greater than 30, where the performance ratio is calculated using the following formula:   TP  =            S              T        xc3x97        E        xc3x97        C              xc3x97    100  
in which:
S=the surface area of the points of adhesive in mm2;
T=the fineness of the warp and weft threads in grams per kilometer (g/km);
E=the mean thickness of the scrim in mm; and
C=the adhesive fraction in the range 0 to 1.
The objects of the present invention are also achieved by means of a method of manufacturing scrim of the present invention, which comprises:
making a grid of non-woven crossed or superposed threads comprising at least two sheets of warp threads between which at least one sheet of weft threads is interposed; and
impregnating the grid of threads with a binder for binding the warp and weft threads together at their cross-points,
wherein the grid of threads is pressed before the stage of drying the binder has terminated.